1. Field of the Invention
This invention relates to light modulating devices (e.g., a polymer-dispersed liquid crystal device hereinafter referred to as a "PDLC device").
2. Description of the Related Art
Various types of light modulating devices are known. One type is the so-called PDLC device that includes an electrically responsive liquid crystal layer in which liquid crystal droplets are dispersed throughout a polymer matrix. One way to prepare the liquid crystal layer is by combining the liquid crystal material with a polymerizable matrix precursor and then subjecting the mixture to polymerization conditions. Polymerization causes phase separation of the liquid crystal material, resulting in the formation of liquid crystal droplets dispersed throughout the polymerized matrix.
PDLC devices are translucent in the absence of an electric field due to light scattering and become transparent upon application of the field. Reverse mode PDLC devices are also known. These devices are transparent in the absence of an electric field and become translucent upon application of the field.
Various PDLC matrices are known. They include the polymerization products of epoxy, isocyanate, and certain photo-curable vinyl monomers (e.g., acrylates or the reaction product of a multi-functional thiol with a multi-functional acrylate or a multi-functional allyl).
During manufacture of the PDLC device, the liquid crystal layer typically is placed in contact with one or more thin film electrodes and then laminated between two rigid protective sheets, e.g., glass sheets. During lamination, the sheets can be distorted by the temperatures and pressures associated with the lamination process. At the conclusion of lamination, the pressure is relieved and the temperature is reduced, allowing the distortions to relax. This relaxation subsequently stresses the liquid crystal layer. If the cohesive strength of the liquid crystal layer and/or the adhesion of the liquid crystal layer to the electrodes is not sufficiently high, the stress will cause the liquid crystal layer to split apart cohesively and/or delaminate from the electrode.
One convenient way to characterize the resistance of a film to delamination or cohesive failure is to measure its T-peel strength. A film with a higher T-peel strength will be much less likely to delaminate or cohesively fail during manufacture.